
const historyMode = 'history';
const hashMode = 'hash';

let _Vue = null;
export default class VueRouter {
  static install(Vue) {
    //1、判断当前插件是否安装
    if (VueRouter.install.installed) {
      return;
    }
    VueRouter.install.installed = true;

    //2、把Vue构造函数记录到全局变量
    _Vue = Vue;
    //3、把创建Vue实例时候传入的router对象注入到Vue实例上
    // _Vue.prototype.$router = this.$options.router

    // 混入
    _Vue.mixin({
      beforeCreate() {
        // router是vue实例， 否则是vue组件
        if (this.$options.router) {
          _Vue.prototype.$router = this.$options.router;
          this.$options.router.init();
        }
      }
    });
  }

  constructor(options) {
    this.options = options;
    this.routeMap = {};
    this.data = _Vue.observable({
      current: options.mode === historyMode ? window.location.pathname : (window.location.hash || '#/') 
    });
  }

  init() {
    this.createRouteMap();
    this.initComponents(_Vue);
    this.initEvent();
  }

  createRouteMap() {
    // 遍历所有的路由规则，把路由规则解析成键值对的形式，存储在routeMap
    this.options.routes.forEach(route => {
      if (this.options.mode === historyMode) {
        this.routeMap[route.path] = route.component;
      } else {
        this.routeMap['#' + route.path] = route.component;
      }
    });
  }

  initComponents(Vue) {
    Vue.component("router-link", {
      props: {
        to: String
      },
      render(h) {
        return h(
          "a",
          {
            attrs: {
              href: this.to
            },
            on: {
              click: this.clickHandler
            }
          },
          [this.$slots.default]
        );
      },
      // runtime版本不支持template
      // template: '<a :href="to"><slot></slot></a>'
      methods: {
        clickHandler(e) {
          if (this.$router.options.mode === historyMode) {
            history.pushState({}, "", this.to);
            this.$router.data.current = this.to;
          } else {
            location.href = '#' + this.to;
            this.$router.data.current = '#' + this.to;
          }
          e.preventDefault();
        }
      }
    });

    const self = this;
    Vue.component("router-view", {
      render(h) {
        const component = self.routeMap[self.data.current];
        return h(component);
      }
    });
  }

  initEvent() {
    if (this.options.mode === historyMode) {
      window.addEventListener("popstate", () => {
        this.data.current = window.location.pathname;
      });
    } else {
      // 页面加载时，设置初始hash  
      window.location.href = this.data.current;
      window.addEventListener('hashchange', (e) => {
        console.log(e);
        this.data.current = window.location.hash;
      })
    }
  }
}
